High frequency heating system



July 5, 1955 O PALMGREN ET AL 2,712,586

HIGH FREQUENCY HEATING SYSTEM Filed May 19, 1955 United HIGH FREQUENCY HEATING SYSTEM Application May N, 1953, Serial No. 356,028 Claims priority, application Sweden May 23, 1952 2 Claims. (Cl. 219-10371) This invention relates to high frequency heating sys tems in working machines particularly for the wood and synthetic resin industry, but also for the metal industry, and more particularly the invention relates to an arrangement for high frequency heating of the work piece in such working machines in which the work piece is continuously advanced along a certain path while being entirely or partially enclosed by usually individually operating implements in the form of carriages, slides or the like, preferably clamping tools, which accompany the work piece. A particular but not exclusive object of the invention is to provide for high frequency heating of the work piece in the glue press described in the United States Patent No. 2,631,622, which discloses a working machine of the type referred to above.

In working machines of such type it is evident that the moving implements or clamps which enclose the work piece makes it diilicult, if not impossible, to let the work piece pass through stationary high frequency impedances so that the work piece thereby in a common manner will be heated. Instead it will be necessary to arrange a high frequency impedance in each separate implement and since the implements will be moving continuously during the heating procedure it is obvious that problems will arise concerning the transmission of the high frequency energy in the most uncomplicated and loss-free manner to the impedance of the moving implements along such a length of the path of the implements that heating of the work piece under a sufficient period of time is obtained. This invention has for its object to give a solution of these problems so that high frequency current heating of the '1 work piece in working machines of the type in question may be readily utilized in a rational way.

The main feature of the invention is that each imple-V ment is equipped with an impedance generating heat in the work piece and connected between an antenna plate carried by said implement and ground in the race for the implements, and that a number of stationary high frequency fed transmission plates is arranged along an arbitrary length of the path of transport of the work piece, which length considerably exceeds the length of each antenna plate in the direction of movement of the implements, said transmission plates being so located relative the antenna plates of the individual implements that high frequency energy is fed capacitively from the transmission plates to the antenna plates during the continuous passage of the latter past the transmission plates, the heat generating impedance in each implement being shunted by a tuning impedance for forming a separate, tuned oscillatory circuit so that the amount of energy transmitted via the antenna plate will be restricted to substantially the amount corresponding to the resistive losses in the oscillatory circuit and particularl" the heat generating impedance.

Hereby energy is fed to the impedance of each continuously moving implement during an arbitrarily chosen part of the path of the latter and this without the necessity of using mechanical current transmitting means such rates Patent ii atented July 5, 1955 ice as sliding contacts or the like and without the risk for are formation when the transmission of energy ceases. A further advantage obtained is that the high frequency generator or generators are not exposed to momentary loads since the antenna plates as Well as the transmission plates of course have a certain extension along the path of the implements and the generator load will thus only gradually increase to its full value when an antenna plate runs in in front of a transmission plate, which usually occurs at a relatively low speed.

The heat generating impedance may of course be an inductance coil, if the work piece is of metal, and in such a case the tuning impedance has to be a variable condenser, but commonly the heat generating impedance is a condenser between the electrodes of which the work piece can serve as a dielectricum and thus become heated and in this latter case the tuning impedance is a variable inductance.

.Further features of the invention will become apparent from the following description of a preferred embodimentdiagrammatically illustrated in the accompanying drawing, where Fig. 1 shows the coupling and working principle of the system while Fig. 2 as an example shows how the details in a separate implement may be formed and connected.

Aided by the information lven in the following text the man of the art will readily understand how the invention may be suitably applied to different working machines of the type indicated.

In Fig. l of the drawing, numeral 1 designates a race consisting of rails or the like which are so placed in the working machine that the desired treatment of the Work piece or pieces can take place. Preferably the race 1 is endless. Along the race a plurality of implements generally designated by the numeral 2 and formed like carriages or slides are arranged to run at a certain distance from each other, so that the implements form a sort of train. Each implement 2 may carry one work piece 3, for instance between clamping tools, or several of the implements may be arranged so as to cooperate for clamping a continuous, glued laminated panel as is the case in the aforementioned patent.

The implements 2, which are working individually, ac-

company the work piece or pieces advanced through the machine and each implement 2 is equipped with two electrodes 4 and 5, which are closely embracing the work piece 3. One 4 of the electrodes is connected to an antenna plate 6, which is carried by the implement 2 and protrudes in a suitable way therefrom, and the other electrode 5 is grounded to the race It via the frame and wheels of the implement. Along the race 1 there is provided a number of stationary, high frequency fed transmission plates 7, each of which is connected to a high frequency generator 8. Each such generator is also grounded to the race 1. The transmission plates 7 are so placed relative to the antenna plates 6 of the individual implements 2 that high frequency energy will be capacitively transmitted to the latter during a part of their path thanks to the fact that each antenna plate 6 with each of he transmission plates '7 form a condenser, which is insulated by air or some other medium with higher dielectric constant and small losses, and such condensers offer only little resistance to the high frequency current.

To reduce the quantity of energy transmitted from the transmission plates 7 to the antenna plates 6 as far as possible and thus also reduce the total electrical losses in the plant, the condenser formed by the two electrodes 4 and 5 of each implement 2 is shunted by means of an adjustable tuning inductance 9, so as to obtain for each implement 2 a separate oscillating circuit including the tuning inductance and the condenser constituted by the electrodes 4 and 5 and the work piece 3. By a suitable adjustment of the inductance 9 this oscillating circuit can be tuned in such a way that a relatively high reactive energy flux is obtained in the circuit and through the work piece 3, whereas the energy transmission to the implement is restricted to the amount needed for covering the resistive losses, i. e. substantially the energy which is directly converted into heat in the work piece 3.

Since both the antenna plate 6 of each implement 2 and the transmission plates 7 have a certain extension in the longitudinal direction of the race 1, the transmission resistance between each transmission plate and each antenna plate will decrease gradually when the implement runs into the zone covered by each transmission plate and also increase gradually when the implement leaves this Zone. In other words, each antenna plate 6 will form not only a condenser with each transmission plate 7 but even a variable condenser and no momentary changes in the load may occur. When an implement 2 is located within a zone covered by a transmission plate 7, high frequency energy will be transmitted from the relating high frequency generator 8 to the transmission plate 7 and from there to the antenna plate 6 and the electrode 4, through the work piece 3 to the electrode 5 and back to the generator 8 through the race 1.

As already indicated, it is necessary in many cases to employ several high frequency generators 8 in order that the heating of the work piece or pieces should be effected along a suiiicient length of the race. If so, each generator should be connected to its own transmission plate 7 and since the implements 2 are arranged to be advanced one after the other so as to form an endless train according to the drawing and since they are always uniformly spaced from each other, the transmission plates 7 are given a length corresponding to a whole multiple (3 in the drawing) of the pitch between the antenna plates 6 of the implements. This offers the advantages that the load of each high frequency generator always remains approximately constant, since each time one implement leaves the zone covered by the transmission plate 7 another implement enters the zone successively at the opposite end thereof. The transmission plates lying one after the other are spaced from each other in the longitudinal direction of the race by an interspace which, calculated from edge to edge, corresponds at least to the length of each antenna plate 6 so that the different high frequency circuits are kept completelyseparate.

If the individual implements of the working machine are equipped with clamping plates between which the work piece is adapted to be kept pressed, each clamping plate may form an electrode of the heat generating condenser impedance. Otherwise, as shown in Fig. 2, each clamping plate 11 may be provided with two branched electrode plates 4' and 5' which are insulated from each other, one of these plates being then grounded and the other connected to the antenna plate 6 as illustrated. Fig. 2 also shows how the tuning inductance 9 may simply consist of two metal wire arms 12 and 13 between which a slightly arched sheet metal strip 14 extends. This strip 14 is displaceable along the arms 12 and 13 for adjusting the inductance at tuning the oscillating circuit.

Of course the more detailed construction of the plant may be varied within wide limits to meet the particular demands on it. It has proved advantageous in practice to use transmission plates 7 consisting of two parallel but slightly spaced metal sheets between which antenna plates 6 rising from the implements enter, and of course there is nothing to prevent that the transmission capacity is increased by making both transmission plates and antenna plates from several metal sheets which enters be tween each other but are well insulated from each other.

We claim:

1. In equipment for simultaneously heating and pressing dielectric work pieces; the combination of a plurality of carriages coupled together to form an endless train, an endless race for said train, means for imparting continuous motion to said train, work compressing means on each of said carriages, said compressing means including a relatively fixed jaw, a relatively movable jaw and means for'urging said movable jaw towards said fixed jaw for compressing a work piece therebetween, spaced heating electrodes mounted on said jaws and facing the work piece, an antenna plate on each of said carriages, said antenna plate being connected to at least one of said heating electrodes of the compressing jaws of the related carriage,-another one of said heating electrodes being grounded to said race, a variable inductance on each of said carriages, said inductance being shunted between said antenna plate and said grounded heating electrode of the related carriage to form with said heating electrodes a separate turnable oscillatory load circuit on each carriage, at least one stationary transmission plate extending along a part of said race and positioned to be closely passed by the respective antenna plates of said moving carriages, and a high frequency oscillator grounded to said race and connected to said transmission plate for transmitting high frequency energy capacitively therefrom to said passing antenna plates and hence to the oscillatory load circuit of each carriage passing said transmission plate thereby causing said load circuit to temporarily produce a relatively high current flow through the compressed work piece in response to a relatively low current flow through the oscillator circuit.

2. In equipment for simultaneously heating and pressing dielectric work pieces; the combination of a plurality of carriages coupled together to form an endless train, an endless race for said train, means for imparting continuous motion to said train, work compressing means on each of said carriages, said compressing means including a relatively fixed jaw, a relatively movable jaw and means for urging said movable jaw towards said fixed jaw for compressing a work piece therebetween, spaced heating electrodes mounted on said jaws and facing the work piece, an antenna plate on each of said carriages, said antenna plate being connected to at least one of said heating electrodes of the compressing jaws of the related carriage, another one of said heating electrodes. being grounded to said race, a variable inductance on each of said carriages, said inductance being shunted betweensaid antenna plate and said grounded heating electrode of the related carriage to form with the heating electrodes a separate, turnable oscillatory load circuit on each carriage, a plurality of stationary, longitudinally spaced apart transmission plates extending along parts of said race and positioned to be successively and closely passed by the antenna plates of said moving carriages, and a plurality of high frequency oscillators each grounded to said race and each connected to a related one of said transmission plates for transmitting high frequency ener'gy capacitively therefrom to said passing antenna plates and hence to the oscillatory load circuit of each carriage passing said transmission plates. the longitudinal distance between said spaced transmission plates being at least as large as the length of said antenna plates of the respective carriages.

References Cited in the file of this patent UNITED STATES PATENTS 2,304,983 Winkley et al. Dec. 15, 1942 2,436,732 Rowe Feb. 24, 1948 2,473,881 Hagopian June 21, 1949 2,546,004 Kinn Mar. 20, 1951 2,631,622 Bergvall et al Mar. 17, 1953 

